1. Field of the Invention
The present invention relates to a process for separation and recovery of cyclopentadiene (hereinafter called CPD), or CPD and methylcyclopentadiene (hereinafter called MCPD) in high purity from cracked gasoline fraction, which is produced as a by-product of ethylene production by thermal or steam cracking of a petroleum fraction such as naphtha, kerosene, and gas oil.
The process of the present invention is advantageous because it allows an economical separation of highly pure CPD, or highly pure CPD and MCPD merely by addition of simple processing units, without any alteration of the process and operating conditions of the conventional process for treatment of cracked gasoline, and also because it reduces the load on the hydrogenation reactor in the benzene-toluene-xylene (hereinafter called BTX) recovery process. The reduction of the load on the hydrogenation reactor not only allows saving of hydrogen consumption in the reactor, but also prolongs the catalyst life.
CPD is a useful material, for example, as a raw material of Diels-Alder reactions, and MCPD also is a useful material. For example, MCPD is used as a hardener of epoxy resins. At present, the production of MCPD is low and MCPD is an expensive material.
2. Description of the Prior Art
In the production of ethylene by thermal or steam cracking of a petroleum fraction such as naphtha, kerosene, and gas oil, the cracked gasoline fraction which is formed as a by-product, is usually processed by two distillation columns in order to recover BTX from the fraction, and the BTX fraction is then passed to an aromatics extraction unit, in which highly pure BTX are recovered.
The cracked gasoline fraction also contains about 3-7% of CPD and about 1-2% of MCPD. However, treatment of CPD is not easy because it is thermally unstable and readily undergoes dimerization and codimerization. Also, the separation of MCPD from cracked gasoline by distillation is not easy because of its low concentration and because its boiling point (73.degree. C.) is close to the boiling point of benzene (80.degree. C.), which is present in large amount in cracked gasoline.
Moreover, the separation and recovery of MCPD is difficult because it is unstable and readily dimerizes or codimerizes with other compounds.
With regards to processes for separation and recovery of CPD and MCPD from cracked gasoline fraction, U.S. Pat. No. 2,733,279 proposes a process which comprises obtaining a C.sub.5 -C.sub.7 fraction by distillation of a cracked gasoline fraction, removing light fractions by heating the fraction, and recovering CPD and MCPD by depolymerization-distillation of the dimers. U.S. Pat. No. 2,733,280 proposes a process which comprises recovering a fraction containing the dimers by distillation under reduced pressure, followed by recovering CPD and MCPD by depolymerization-distillation of the dimers.
However, the contents of CPD and MCPD in cracked gasoline are only in the range of about 3-7% and 1-2%, respectively, and because of their low contents, a large amount of cracked gasoline should be processed, which requires a large apparatus for this process, and a large amount of energy is required for the distillation, dimerization, and depolymerization processes. Therefore, these processes are economically not advantageous.